Use of Cell-Edge FDD Coverage to Separate Cell-Center TDD Coverage From Adjacent TDD Coverage with Conflicting TDD Configuration

ABSTRACT

In a system where a first node provides a first area of TDD coverage on a first TDD carrier using a first TDD configuration and an adjacent second node provides a second area of TDD coverage on a second TDD carrier using a different second TDD configuration, the first node could additionally provide an area of FDD coverage on a first FDD carrier, including causing the area of FDD coverage to sit at least partially between the first and second areas of TDD coverage and therefore to define a spatial buffer between the first and second areas of TDD coverage. For instance, the first access node could restrict its service on the first TDD carrier to be for user equipment devices (UEs) that are relatively close to the first access node and could restrict its service on the first FDD carrier to be for UEs that are relatively far away from the first access node.

REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 17/204,654,filed Mar. 17, 2021, the entirety of which is hereby incorporated byreference.

BACKGROUND

A typical cellular wireless network includes a number of access nodesconfigured to provide wireless coverage areas in which to serve userequipment devices (UEs) such as cell phones, tablet computers, trackingdevices, embedded wireless modules, and other wirelessly equippeddevices (whether or not user operated). In turn, each access node couldsit as a node on a core access network that includes entities such as anetwork controller and a gateway system providing connectivity with oneor more external transport networks such as the Public SwitchedTelephone Network (PSTN) and/or the Internet. With this arrangement, aUE within coverage of the system could engage in air interfacecommunication with an access node and could thereby communicate via theaccess node with various remote network entities or with other UEsserved by the access node.

Such a network could operate in accordance with a particular radioaccess technology (RAT), with air-interface communications from theaccess nodes to UEs defining a downlink or forward link andair-interface communications from the UEs to the access nodes definingan uplink or reverse link.

Over the years, the industry has developed various generations of RATs,in a continuous effort to increase available data rate and quality ofservice for end users. These generations have ranged from “1G,” whichused simple analog frequency modulation to facilitate basic voice-callservice, to “4G”—such as Long Term Evolution (LTE), which nowfacilitates mobile broadband service using technologies such asorthogonal frequency division multiplexing (OFDM) and multiple inputmultiple output (MIMO). And recently, the industry has completed initialspecifications for in “5G” and particularly “5G NR” (5G New Radio),which may use a scalable OFDM air interface, advanced channel coding,massive MIMO, beamforming, and/or other features, to support higher datarates and countless applications, such as mission-critical services,enhanced mobile broadband, and massive Internet of Things (IoT).

In accordance with the RAT, each access node could provide service onone or more carriers, with each carrier spanning one or moreradio-frequency (RF) channels for carrying communications wirelesslybetween the access node and UEs. In particular each carrier could befrequency division duplex (FDD), defining separate frequency channelsfor downlink and uplink use, or time division duplex (TDD), defining asingle frequency channel multiplexed over time between downlink anduplink use.

Each such frequency channel could be characterized by its position andwidth in RF spectrum, such as by a designated center frequency andbandwidth. Further, each channel could be structured to define variousphysical resources for carrying communications. For instance, under anexample radio access technology, each channel could be divided over timeinto frames, subframes, timeslots, and symbol segments, and could bedivided over frequency into subcarriers. As a result, each channel coulddefine an array of time-frequency resource elements in which subcarrierscan be modulated to carry data communications. Further, within eachsubframe and timeslot, these resource elements could be divided intogroups defining physical resource blocks (PRBs) that could be allocatedto carry data on an as-needed basis. And certain resource elements maybe reserved for other special purposes, such as to carry control channelsignaling for instance.

Each carrier could be defined within an industry standard frequencyband, by its frequency channel(s) being defined within the frequencyband. Examples of such frequency bands include, without limitation, (i)Band 25, which supports FDD carriers and extends from 1850 MHz to 1915MHz on the uplink and 1930 MHz to 1995 MHz on downlink, (ii) Band 26,which supports FDD carriers and extends from 814 MHz to 849 MHz on theuplink and 859 MHz to 894 MHz on the downlink, (iii) Band 71, whichsupports FDD carriers and extends from 663 MHz to 698 MHz on the uplinkand 617 MHz to 652 MHz on the downlink, (iv) Band 41, which supports TDDcarriers and extends from 2496 MHz to 2690 MHz, (v) Band n260, whichsupports TDD carriers and extends from 27 GHz to 40 GHz, and (vi) Bandn261, which supports TDD carriers and extends from 27.5 GHz to 28.35GHz.

Further, each access node could have a respective antenna structure thatis configured to transmit and receive electromagnetic signals on one ormore such carriers in a region defined by an antenna pattern orradiation pattern. The antenna pattern could define a geographic scopeof coverage in which the access node can engage in downlink transmissionto UEs and receive uplink transmission from UEs.

Thus, a coverage area provided by an access node could be characterizedin the frequency domain by the coverage area's carrier and in thespatial domain by the coverage area's geographic scope of coverage.

Overview

When an access node's coverage area operates on a TDD carrier, thecarrier could be structured with a particular TDD configuration (frameconfiguration) defining a sequence of equal-duration subframes andestablishing which subframes are for downlink use and which subframesare for uplink use. Further, the TDD configuration may designate certainsubframes as special subframes that are part downlink and part downlink,to help facilitate transition from downlink to uplink operation. Thus, arepresentative TDD configuration could establish for each subframe perframe whether the subframe is a downlink subframe (D), an uplinksubframe (U), or a special subframe (S).

Various TDD configurations could be feasible. In LTE, for instance, theair interface on a TDD carrier defines a continuum of 10-millisecondframes, each divided into ten 1-millisecond subframes, and LTE definesseven standard TDD configurations as set forth in Table 1.

TABLE 1 Subframe Number (0-9) TDD Configuration 0 1 2 3 4 5 6 7 8 9 0 DS U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 D S U UU D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U U U D SU U DNon-standard implementations and/or other radio access technologies maydefine these or other frame structures and other TDD configurations aswell.

In practice, an access node that provides a coverage area on a carrierhaving any such TDD configuration could broadcast in the coverage area asystem information message that specifies the carrier's TDDconfiguration, so that UEs served by the access node in the coveragearea could determine the TDD configuration and operate accordingly. Forinstance, an access node could broadcast a System Information Block(SIB) message in subframe 0 of each frame and could include in the SIBmessage a specification of the carrier's TDD configuration, such as aframe configuration (FC) number. Thus, a UE that is within that coveragearea of the access node could read that broadcast SIB message todetermine the TDD configuration of the coverage area's carrier.Alternatively, a UE might determine the TDD configuration of a carrierin other ways, such as by monitoring to determine the subframes in whichthe access node transmits per frame.

In an example cellular wireless network, each access node providingcoverage on a TDD carrier could be configured to operate with aparticular TDD configuration on that carrier. Each such TDDconfiguration could be statically set by engineering design or the like.Or alternatively, the TDD configuration could be set dynamically to helpaccommodate varying traffic profiles. For example, at times when anaccess node serves heavier downlink traffic, the access node mayconfigure the TDD carrier to have a more downlink-centric TDDconfiguration such as FC2, FC4, or FC5. Whereas, at times when theaccess node serves heavier uplink traffic, the access node may configurethe TDD carrier to have a more uplink-centric TDD configuration such asFC0, FC1, or FC6.

One technological issue with TDD operation is that, if two adjacentaccess nodes provide spatially overlapping coverage on the same TDDcarriers as each other but that use different TDD configurations thaneach other, interference can occur when there is concurrently downlinkcommunication in one access node's coverage area and uplinkcommunication in the other access node's coverage area.

Disclosed herein is a mechanism that may help to address this issue byhaving at least one of the access nodes implement a guard zone of FDDcoverage spatially between the conflicting TDD coverage areas i.e., tohelp spatially separate the conflicting TDD coverage areas from eachother.

In accordance with the disclosure, when a first access node will providefirst TDD coverage on a TDD carrier using a first TDD configuration anda second access node that is spatially adjacent to the first access nodewill provide second TDD coverage on the same TDD carrier but using asecond TDD configuration that is different than the first TDDconfiguration, at least the first access node will be configured toadditionally provide an area of FDD coverage that at least partiallysits spatially between the first TDD coverage and the second TDDcoverage and thus defines a buffer between those TDD coverage areas.

To do this in practice, the first access node could be configured toprovide coverage on both the TDD carrier and an FDD carrier and furtherto (i) restrict service on the TDD carrier to cell-center UEs, i.e., UEsrelatively close to the first access node and (ii) restrict service onthe FDD carrier to cell-edge UEs, i.e., UEs relatively distant from thefirst access node. This way, the first access node could define an outerband of effective FDD coverage that exists spatially beyond the firstaccess node's area of TDD coverage and that sits at least partiallybetween the first access node's TDD coverage and the second accessnode's TDD coverage.

In addition, the second access node could also be configured similarlyto provide a respective are of FDD coverage that at least partially sitsbetween the first TDD coverage and the second TDD coverage and that,cooperatively with the area of FDD coverage provided by the first accessnode, defines a buffer between the access nodes' TDD coverage areas.

These as well as other aspects and advantages will become apparent tothose of ordinary skill in the art by reading the following detaileddescription, with reference where appropriate to the accompanyingdrawings. Further, it should be understood that the descriptionsprovided in this overview and below are intended to illustrate theinvention by way of example only and not by way of limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a wireless communication networkin which the coverage shown in FIG. 1 could be provided.

FIG. 2 illustrates two example configurations of TDD coverage areas withconflicting TDD configurations.

FIG. 3 illustrates examples of how an FDD guard zone could be introducedas a spatial buffer between the conflicting TDD coverage areas of FIG. 2.

FIG. 4 is a simplified block diagram of an example access node.

DETAILED DESCRIPTION

As noted above, FIG. 1 is a simplified block diagram of an examplewireless communication network in which the disclosed principles couldbe applied. It will be understood, however, that variations from thisand other arrangements and processes described are possible. Forinstance, various described entities, connections, functions, and otherelements could be added, omitted, distributed, re-located, re-ordered,combined, or changed in other ways. In addition, operations described asbeing performed by one or more entities could be implemented in variousways, such as by a processing unit executing instructions stored innon-transitory data storage, along with associated circuitry or otherhardware, for instance.

FIG. 1 depicts two example access nodes 12, 14 included in the examplenetwork. These access nodes could be operated by a common wirelessservice provider. The wireless service provider could thus configure theaccess nodes for service.

Each access node could be a macro access node, a small cell access node,or other type of access node designed to provide wireless coverage inwhich to serve user UEs in accordance with one or more defined RATs, andthe access nodes could differ in form from each other. Further, in linewith the discussion above, each access node could have a respectivewireless communication interface, including one or more radios andantenna structures configured to transmit and receive electromagneticsignals so as to provide respective coverage in which to serve UEs.

In the illustrated arrangement, each access node is shown operatingrespectively on at least two carriers, including a TDD carrier and anFDD carrier. Namely, access node 12 is shown operating on a TDD carrier16 and an FDD carrier 18, and access node 14 is shown operating operateon a TDD carrier 20 and an FDD carrier 22. In an example implementation,the TDD carriers 16, 20 could be the same as each other, i.e., occupyingthe same frequency channel as each other. Alternatively, the TDDcarriers could be partially the same as each other (e.g., with theirfrequency channels partially overlapping with each other) or adjacent toeach other (e.g., with their frequency channels being adjacent to eachother). The FDD carriers 18, 22, on the other hand, may or may not bethe same, overlapping, or adjacent to each other in frequency.

The air interface on each of these carriers could be structured asdescribed above, among other possibilities. For instance, the airinterface on the frequency channel of each TDD carrier and on thedownlink and uplink frequency channels of each FDD carrier,respectively, could be divided over time into frames, subframes,timeslots, and symbol time segments, and over frequency intosubcarriers, thus defining an array of air-interface resource elementsgrouped into PRBs allocable by the access node as noted above, for useto carry data to or from served UEs.

As further shown, access nodes 12, 14 are interconnected with one ormore core networks 24, which could provide connectivity with one or moreexternal transport networks 26 such as the Internet for instance. Eachsuch core network could take various forms, examples of which includewithout limitation an Enhanced Packet Core (EPC) network and a NextGeneration Core (NGC) network.

In an example EPC arrangement as shown, the core network includes amobility management entity (MME) 28, a serving gateway (SGW) 30, and apacket-data-network gateway (PGW) 32, among other nodes. With thisarrangement, each access node could have a communication interface withthe MME, with the SGW, and with the each other access node, the MMEcould have a communication interface with the SGW. Further, the SGWcould have a communication interface with the PGW, and the PGW couldprovide connectivity with the transport network 26.

FIG. 1 also illustrates various example UEs 34 that may from time totime be within coverage of the network. These UES could be any of thetypes noted above, among other possibilities, each including one or moreradios and associated logic that enables the UE to be served inaccordance with one or more RATs such as one of those noted above forinstance.

In line with the discussion above, upon entering into coverage of thenetwork, each such UE could initially scan for coverage and could detectthreshold strong coverage of an access node on a given carrier in agiven band. For instance, the UE could evaluate reference signal receivepower (RSRP) from the access node on the carrier and determine that thatRSRP is strong enough to justify connecting. Further, if the UE detectsthreshold strong coverage of multiple access nodes and/or on multiplecarriers, the UE might select the strongest detected coverage on whichto connect.

In addition, if the UE is not yet registered for service with the corenetwork 24, the UE could engage in attachment signaling with the MME viathe access node. And after authenticating the UE, the MME couldresponsively coordinate setup of one or more user-plane bearers betweenthe UE and the PGW, including for each a data radio bearer over the airbetween the access node and the UE and an access bearer through the corenetwork between the access node and the PGW.

Once the UE is connected with the access node on a carrier and isregistered for service, the access node could then serve the UE on thecarrier, coordinating use of air interface resources such as PRBs tocarry data to and from the UE. For instance, when packet data arrives atthe core network 24 for transmission to the UE, that packet data couldflow over an appropriate bearer to the access node, and the access nodecould schedule and provide transmission of the packet data to the UE onone or more downlink PRBs of the carrier. And when the UE has packetdata to transmit, the UE could transmit a scheduling request to theaccess node, the access node could direct the UE to transmit the data onone or more uplink PRBs of the carrier, and the UE could accordinglytransmit the data on the indicated uplink PRB(s), and the access nodecould forward the data over an appropriate bearer for output on thetransport network 24.

While a UE is served by an access node on a given carrier, the UE mayalso regularly monitor the UE's coverage strength on that carrier and onother carriers and may provide the access node with measurement reportsto enable the access node to adapt its service of the UE based at leaston the UE's coverage conditions.

For instance, the UE could periodically, and/or in response to varioustriggers, measure and report to the access node the UE's RSRP on thecarrier on which the UE is connected with the access node and/or on oneor more other carriers, and the access node may use these RSRP reportsas a basis to control whether to hand over the UE to another accessnode. For example, if the UE's RSRP from the access node becomesthreshold low and the UE detects threshold strong (e.g., thresholdstronger) coverage from another access node, the UE's serving accessnode may coordinate handover of the UE to that other access node.

In line with the discussion above, access nodes 12, 14 could usedifferent TDD configurations than each other on their respective TDDcarriers 16, 20. For instance, for coverage on TDD carrier 16, accessnode 12 may use one of the TDD configurations shown above in Table 1,and for coverage on TDD carrier 20, access node 14 may use a differentone of the TDD configurations shown above in Table 1. Alternatively, theTDD configurations used by the access nodes could differ from each otherin other ways, perhaps with respect to downlink-uplink sequencing and/orsubframe definitions, among other possibilities. Further, as discussedabove, each access node could broadcast on its TDD carrier an indicationof the TDD configuration of the TDD carrier, and the access node and UEsin coverage of that TDD carrier could operate accordingly.

In the example arrangement, given that these two adjacent access nodesprovide respective coverage with different TDD configurations than eachother, interference can occur where one access node's TDD coverage isdownlink and the other access node's TDD coverage is uplink. Withoutlimitation, an example of such interference could occur at a momentwhere a UE served by one access node provides uplink transmission on thecarrier, and where that uplink transmission interferes with downlinktransmission that another nearby UE served by the other access node isattempting to receive. Other examples could exist as well.

FIG. 2 illustrates two examples of this problematic arrangement. In oneexample as shown in part A, access node 12 and access node 14 eachprovide generally omnidirectional coverage on their respective TDDcarriers 16, 20, and the TDD coverage of access node 12 overlaps in partwith the TDD coverage of access node 14. And in another example as shownin part B, access node 12 and access node 14 each provide moredirectional coverage on their respective TDD carriers, with each accessnode's TDD coverage being directed toward the other access node, andwith their respective TDD coverage areas overlapping with each other.

As presently contemplated, either or both of these access nodes could beconfigured to help avoid this spatial overlap of their TDD coverageareas, by introducing an FDD guard zone that sits spatially between theaccess nodes' respective TDD coverage areas. In particular, one or bothof the access nodes could provide an area of FDD coverage that sits atleast partially between the two access nodes' areas of TDD coverage,such that this area of FDD coverage effectively defines a buffer betweenthe access nodes' TDD coverage areas.

An access node that provides or contributes to defining this FDD guardzone could optimally do so by limiting service on the access node's TDDcarrier to be for UEs that are relatively close to the access node andlimiting service on the access node's FDD carrier to be for UEs that arerelatively far away from the access node, thus effectively defining anouter spatial band of FDD service—even though the access node's FDDcoverage emanates from the access node and may thus technically coverUEs that are relatively close to the access node.

FIG. 3 illustrates some non-limiting examples of how this FDD guard zonecould be structured, as variations from the example arrangements of FIG.2 .

As shown in part A of FIG. 3 , where each access node providesomnidirectional coverage on both TDD and FDD, each access node could beconfigured to provide an inner zone of TDD service and an outer zone ofFDD service, and the access nodes' zones of FDD service could beconfigured to overlap with each other and cooperatively to sit at leastpartially between the access node's respective zones of TDD service. Tofacilitate this, in practice, each access node could limit service onits TDD carrier to be for UEs that are relatively close to the accessnode and could limit service on its FDD carrier to be for UEs that arerelatively far away from the access node, defining one or morethresholds for “close to” and “far away” in a manner that puts theaccess nodes' zones of FDD service cooperatively at least partiallybetween the access nodes' zones of TDD coverage.

In an alternative embodiment in this example, just one of the accessnodes could provide such an outer zone of FDD service to achieve largelythe same effect.

As shown in part B of FIG. 2 , where each access node provides moredirectional coverage on both TDD and FDD, each access node couldlikewise be configured to provide an inner zone of TDD service and anouter zone of FDD service, and the access nodes' zones of FDD servicecould be configured to overlap each other and to cooperatively sit atleast partially between the two access nodes' respective zones of TDDservice. To facilitate this, in practice, each access node couldlikewise limit service on its TDD carrier to be for UEs that arerelatively close to the access node and could limit service on its FDDcarrier to be for UEs that are relatively far away from the access node,similarly defining one or more thresholds for “close to” and “far away”in a manner that puts the access node's zone of FDD service at leastpartially between the two access nodes' zones of TDD coverage.

And here too in an alternative embodiment here, just one of the accessnodes could provide such an outer zone of FDD service to achieve largelythe same effect.

Note also that an access node's outer zone of FDD service need notitself sit fully between that access node's zone of TDD service and theother access node's zone of TDD service. Rather, as long as the accessnode's outer zone of FDD service at least partially covers an area thatsits between the two access nodes' zones of TDD service, thus acting asa spatial buffer between the access nodes' zones of TDD service, it isalso possible that the access node's outer zone of FDD service mayoverlap to some extent with its or the other access node's zone of TDDservice.

Further, while FIG. 2 shows clearly lines of demarcation between anaccess node's TDD zone of service and the access node's FDD zone ofservice, the separation of those zones may be less clear in practice.

In an example implementation, an access node could operate in variousways to limit its outer zone of FDD service to be for UEs that arerelatively far away from the access node and to limit its inner zone ofTDD coverage to be for UEs that are relatively close to the access node.

First, the access node could define the access node's FDD coverage tophysically extend farther from the access node than the access node'sTDD coverage, so that, as to those two carriers, UEs that are positionedphysically farther away from the access node than the range of theaccess node's TDD coverage could be served by the access node on justthe access node's FDD carrier. The access node could so define its FDDcoverage to extend farther from the access node than the access node'sTDD coverage by broadcasting a higher power reference signal on theaccess node's FDD carrier than on the access node's TDD carrier and/orby other settings such as having greater antenna downtilt for RFradiation on the TDD carrier than on the FDD carrier. Further, path lossdifference between the FDD carrier and TDD carrier could contribute tohaving the FDD coverage extend farther from the access node than the TDDcoverage.

Second, the access node could take into account UE geolocation and/or UEreported coverage strength as a basis to limit the access node's outerzone of FDD service to be for UEs that are relatively far away from theaccess node and to limit the access node's inner zone of TDD service tobe for UEs that are relatively close to the access node.

By way of example, the when a UE is connected with the access node oneither carrier, the access node could determine the geolocation of theUE (by using a standard geolocation-determination technique) and coulddetermine whether that geolocation is within the area that is deemed tobe the outer zone of FDD service, defined for present purposes forinstance, i.e., whether the UE is located at least threshold far awayfrom the first access node. If so, then the access node could cause theUE to be served on the FDD carrier rather than on the TDD carrier;whereas, if not, then the access node could cause the UE to be served onthe TDD carrier rather than on the FDD carrier.

With this process, a UE that is close enough to the access node to bewithin coverage of the access node on both the access node's TDD carrierand the access node's FDD carrier would be restricted to being served onthe TDD carrier—even though the UE could just as well be served on theFDD carrier.

Alternatively or additionally, the access node could compare the UE'sreported RSRP (or other coverage-strength measure) from the access nodewith a threshold that is defined by engineering design or otherwise torepresent a demarcation between the area that is deemed to be the innerzone of TDD service and the area that is deemed to be the outer zone ofFDD service. If the access node determines that the UE's coveragestrength is low enough to indicate that the UE is likely far enough awayfrom the access node to be in the area deemed to be the outer zone ofFDD service, then the access node could cause the UE to be served on theFDD carrier rather than on the TDD carrier. Whereas, if the access nodedetermines that the UE's coverage strength is high enough to indicatethat the UE is likely close enough to the access node to be in the areadeemed to be the inner zone of TDD service, then the access node couldcause the UE to be served on the TDD carrier rather than on the FDDcarrier.

With this process as well, a UE that is in strong enough coverage of theaccess node on both the access node's TDD carrier and the access node'sFDD carrier would be restricted to being served on the TDD carrier—eventhough the UE could just as well be served on the FDD carrier.

In either of these or other implementations, to cause the UE to beserved on a desired one of the carriers rather than on the othercarrier, the access node could determine whether the UE is alreadyserved by the access node on the desired carrier and could actaccordingly. If the access node determines that the UE is already servedby the access node on the desired carrier, then the access node couldcause the UE to continue being served by the access node on that carrierby not responsively transitioning the UE to be served instead by theaccess node on the other carrier. Whereas, if the access node determinesthat the UE is not already served by the access node on the desiredcarrier, then the access node can cause the UE to transition to beserved by the access node instead on the desired carrier, such as bytransmitting to the UE an RRC connection-reconfiguration messagedirecting the UE accordingly and updating a context record or the likeaccordingly, among other possibilities.

Accordingly, the above arrangement and process could facilitate use ofconflicting TDD configurations in a wireless communication system inwhich a first access node provides a first area of TDD coverage on afirst TDD carrier using a first TDD configuration and in which a secondaccess node adjacent to the first access node provides a second area ofTDD coverage on a second TDD carrier using a second TDD configurationdifferent than the first TDD configuration.

For instance, in that context, the first access node could provide firstarea of FDD coverage on a first FDD carrier, including causing the firstarea of FDD coverage to sit at least partially between the first area ofTDD coverage and the second area of TDD coverage and therefore to definea spatial buffer between the first area of TDD coverage and the secondarea of TDD coverage.

In line with the discussion above, the act of the first access nodecausing the first area of FDD coverage to sit at least partially betweenthe first area of TDD coverage and the second area of TDD coverage couldinvolve (i) restricting service by the first access node on the firstTDD carrier to be for UEs that are relatively close to the first accessnode and (ii) restricting service by the first access node on the firstFDD carrier to be for UEs that are relatively far away from the firstaccess node.

Further, as discussed above, the act of restricting service by the firstaccess node on the first FDD carrier to be for UEs that are relativelyfar away from the first access node could involve (i) determining that adistance of a UE from the first access node is at least as short as apredefined threshold distance and (ii) responsive to the determining,causing the UE to be served by the first access node on the first TDDcarrier rather than on the first FDD carrier.

Here, for instance, the process could involve setting the predefinedthreshold distance at a level that helps to situate the first area ofFDD coverage at least partially between the first area of TDD coverageand the second area of TDD coverage. And the act of causing the UE to beserved by the first access node on the first TDD carrier rather than onthe first FDD carrier could involve (i) if the UE is currently served bythe first access node on the first TDD carrier rather than on the firstFDD carrier, then continuing to serve the UE on the first TDD carrier,and (ii) if the UE is currently served by the first access node on thefirst FDD carrier rather than on the first TDD carrier, thentransitioning the UE from being served by the first access node on thefirst FDD carrier to being served instead by the first access node onthe first TDD carrier.

Alternatively, as discussed above, the act of restricting service by thefirst access node on the first FDD carrier to be for UEs that arerelatively far away from the first access node could involve (i)determining that coverage strength detected by a UE from the firstaccess node is at least as strong as a predefined threshold coveragestrength and (ii) responsive to the determining, causing the UE to beserved by the first access node on the first TDD carrier rather than onthe first FDD carrier.

And here, the process could likewise involve setting the predefinedthreshold coverage strength at a level that helps to situate the firstarea of FDD coverage at least partially between the first area of TDDcoverage and the second area of TDD coverage. And the act of causing theUE to be served by the first access node on the first TDD carrier ratherthan on the first FDD carrier could involve (i) if the UE is currentlyserved by the first access node on the first TDD carrier rather than onthe first FDD carrier, then continuing to serve the UE on the first TDDcarrier and (ii) if the UE is currently served by the first access nodeon the first FDD carrier rather than on the first TDD carrier, thentransitioning the UE from being served by the first access node on thefirst FDD carrier to being served instead by the first access node onthe first TDD carrier.

Further, as discussed above, the first TDD carrier and second TDDcarrier could be the same as each other. That is, the first TDD carriercould define a range of RF spectrum, and the second TDD carrier coulddefine the same range of RF spectrum. Alternatively, the two TDDcarriers could just partially overlap with each other in RF spectrum orcould be adjacent to each other in RF spectrum or otherwise configuredsuch that there might be some effective overlap.

In addition, as discussed above, the first TDD configuration coulddefine a first sequence of downlink and uplink time intervals, thesecond TDD configuration could define a second sequence of downlink anduplink time intervals, and the first and second TDD configurations coulddiffer from each other in various ways. For instance, there could be atleast one time interval when one of the first and second TDDconfigurations is downlink and the other of the first and second TDDconfigurations is uplink.

Still further, as discussed above, the process could additionallyinvolve configuring the second access node to additionally provide asecond area of FDD coverage, including causing the second area of FDDcoverage to also sit at least partially between the first area of TDDcoverage and the second area of TDD coverage and therefore to contributeto defining the spatial buffer between the first area of TDD coverageand the second area of TDD coverage.

FIG. 4 is next a simplified block diagram of an example access node thatcould be configured to carry out various features described herein. Thisaccess node could be one of the access nodes 12, 14, discussed above,among other possibilities.

As shown in FIG. 4 , the example access node includes a wirelesscommunication interface 36, a backhaul communication interface 38, and acontroller 40, all of which could be integrated together and/orcommunicatively linked together by a system bus, network, or otherconnection mechanism 42.

In an example implementation, the wireless communication interface 36could support air-interface communication and could therefore comprisean antenna structure 44, which could be tower mounted or could takeother forms, and associated components such as a power amplifier and awireless transceiver, so as to facilitate providing coverage and serviceon a TDD carrier and on an FDD carrier. And the backhaul communicationinterface 38 could comprise a wired or wireless communication module,such as an Ethernet network communication module and associated logic,through which the access node could engage in backhaul communicationwith various other network entities.

Further, the controller 40 could be configured to carry out variousoperations described herein. For instance, as shown, the controller 40could include at least one processor 46, such as one or more processors(e.g., one or more general purpose processors and/or specializedprocessors), and a non-transitory data storage 48 (e.g., one or morevolatile and/or non-volatile storage components (e.g., magnetic,optical, or flash storage, necessarily non-transitory)) storing programinstructions 50 executable by the at least one processor 44 to carry outthose operations (e.g., to cause the access node to carry out theoperations).

In the process described above, for example, if the depicted access nodeis the first access node, then, in addition to providing the first areaof TDD coverage on the first TDD carrier using the first TDDconfiguration, the access node could be configured to provide a firstarea of FDD coverage on a first FDD carrier, including causing the firstarea of FDD coverage to sit at least partially between the first area ofTDD coverage and the second area of TDD coverage and therefore to definea spatial buffer between the first area of TDD coverage and the secondarea of TDD coverage. And as discussed above, the act of causing thefirst area of FDD coverage to sit at least partially between the firstarea of TDD coverage and the second area of TDD coverage could involve(i) restricting service by the first access node on the first TDDcarrier to be for user UEs that are relatively close to the first accessnode and (ii) restricting service by the first access node on the firstFDD carrier to be for UEs that are relatively far away from the firstaccess node.

And in the process described above, if the depicted access node is thesecond access node, then, in addition to providing the second area ofTDD coverage on the second TDD carrier using the second TDDconfiguration different than the first TDD configuration, the accessnode could be configured to provide a second area of FDD coverage thatalso sits at least partially between the first area of TDD coverage andthe second area of TDD coverage and therefore contributes to definingthe spatial buffer between the first area of TDD coverage and the secondarea of TDD coverage.

Various other features described herein can be carried out in thiscontext as well, and vice versa.

Further, the present disclosure also contemplates a non-transitorycomputer-readable medium having encoded thereon (e.g., storing,embodying, containing, or otherwise incorporating) program instructionsexecutable to cause a processing unit to carry out operations such asthose described above.

Exemplary embodiments have been described above. Those skilled in theart will understand, however, that changes and modifications may be madeto these embodiments without departing from the true scope and spirit ofthe invention.

What is claimed is:
 1. A method comprising: providing by a first accessnode a time-division-duplex (TDD) coverage area on a TDD carrier; andproviding by the first access node, concurrently with the providing ofTDD coverage area, a frequency-division-duplex (FDD) coverage area on anFDD carrier, including causing the FDD coverage area to sit at leastpartially between the TDD coverage area and a coverage area provided byan adjacent second access node, wherein causing the FDD coverage area tosit at least partially between the TDD coverage area and the coveragearea provided by the adjacent second access node comprises (i)restricting service by the first access node on the TDD carrier to befor user equipment devices (UEs) that are relatively close to the firstaccess node and (ii) restricting service by the first access node on theFDD carrier to be for UEs that are relatively far away from the firstaccess node.
 2. The method of claim 1, wherein restricting service bythe first access node on the FDD carrier to be for UEs that arerelatively far away from the first access node comprises: determiningthat a distance of a UE from the first access node is at least as shortas a predefined threshold distance; and responsive to the determining,causing the UE to be served by the first access node on the TDD carrierrather than on the FDD carrier.
 3. The method of claim 2, furthercomprising setting the predefined threshold distance at a level thathelps to situate the FDD coverage area at least partially between theTDD coverage area and the coverage area provided by the second accessnode.
 4. The method of claim 2, wherein causing the UE to be served bythe first access node on the TDD carrier rather than on the FDD carriercomprises: if the UE is currently served by the first access node on theTDD carrier rather than on the FDD carrier, then continuing to serve theUE on the TDD carrier; and if the UE is currently served by the firstaccess node on the FDD carrier rather than on the TDD carrier, thentransitioning the UE from being served by the first access node on theFDD carrier to being served instead by the first access node on the TDDcarrier.
 5. The method of claim 1, wherein restricting service by thefirst access node on the FDD carrier to be for UEs that are relativelyfar away from the first access node comprises: determining that coveragestrength detected by a UE from the first access node is at least asstrong as a predefined threshold coverage strength; and responsive tothe determining, causing the UE to be served by the first access node onthe TDD carrier rather than on the FDD carrier.
 6. The method of claim5, further comprising setting the predefined threshold coverage strengthat a level that helps to situate the FDD coverage area at leastpartially between the TDD coverage and the coverage area provided by thesecond access node.
 7. The method of claim 5, wherein causing the UE tobe served by the first access node on the TDD carrier rather than on theFDD carrier comprises: if the UE is currently served by the first accessnode on the TDD carrier rather than on the FDD carrier, then continuingto serve the UE on the TDD carrier; and if the UE is currently served bythe first access node on the FDD carrier rather than on the TDD carrier,then transitioning the UE from being served by the first access node onthe FDD carrier to being served instead by the first access node on theTDD carrier.
 8. An access node comprising: a wireless communicationinterface; a backhaul communication interface; and a controller, whereinthe controller is configured to cause the access node to carry outoperations including: providing a time-division-duplex (TDD) coveragearea on a TDD carrier, and providing, concurrently with the providing ofTDD coverage area, a frequency-division-duplex (FDD) coverage area on anFDD carrier, including causing the FDD coverage area to sit at leastpartially between the TDD coverage area and a coverage area provided byan adjacent second access node, wherein causing the FDD coverage area tosit at least partially between the TDD coverage area and the coveragearea provided by the adjacent second access node comprises (i)restricting service by the first access node on the TDD carrier to befor user equipment devices (UEs) that are relatively close to the firstaccess node and (ii) restricting service by the first access node on theFDD carrier to be for UEs that are relatively far away from the firstaccess node.
 9. The access node of claim 8, wherein the controllercomprises at least one processor, non-transitory data storage, andprogram instructions stored in the non-transitory data storage andexecutable by the at least one processor to cause the access node tocarry out the operations.
 10. The access node of claim 9, whereinrestricting service by the first access node on the FDD carrier to befor UEs that are relatively far away from the first access nodecomprises: determining that a distance of a UE from the first accessnode is at least as short as a predefined threshold distance; andresponsive to the determining, causing the UE to be served by the firstaccess node on the TDD carrier rather than on the FDD carrier.
 11. Theaccess node of claim 10, further comprising setting the predefinedthreshold distance at a level that helps to situate the FDD coveragearea at least partially between the TDD coverage area and the coveragearea provided by the second access node.
 12. The access node of claim10, wherein causing the UE to be served by the first access node on theTDD carrier rather than on the FDD carrier comprises: if the UE iscurrently served by the first access node on the TDD carrier rather thanon the FDD carrier, then continuing to serve the UE on the TDD carrier;and if the UE is currently served by the first access node on the FDDcarrier rather than on the TDD carrier, then transitioning the UE frombeing served by the first access node on the FDD carrier to being servedinstead by the first access node on the TDD carrier.
 13. The access nodeof claim 9, wherein restricting service by the first access node on theFDD carrier to be for UEs that are relatively far away from the firstaccess node comprises: determining that coverage strength detected by aUE from the first access node is at least as strong as a predefinedthreshold coverage strength; and responsive to the determining, causingthe UE to be served by the first access node on the TDD carrier ratherthan on the FDD carrier.
 14. The access node of claim 13, wherein theoperations additionally include setting the predefined thresholdcoverage strength at a level that helps to situate the FDD coverage areaat least partially between the TDD coverage and the coverage areaprovided by the second access node.
 15. A non-transitorycomputer-readable medium having stored thereon instructions executableby at least one processor to cause an access node to carry outoperations comprising: providing a time-division-duplex (TDD) coveragearea on a TDD carrier; and providing, concurrently with the providing ofTDD coverage area, a frequency-division-duplex (FDD) coverage area on anFDD carrier, including causing the FDD coverage area to sit at leastpartially between the TDD coverage area and a coverage area provided byan adjacent second access node, wherein causing the FDD coverage area tosit at least partially between the TDD coverage area and the coveragearea provided by the adjacent second access node comprises (i)restricting service by the first access node on the TDD carrier to befor user equipment devices (UEs) that are relatively close to the firstaccess node and (ii) restricting service by the first access node on theFDD carrier to be for UEs that are relatively far away from the firstaccess node.
 16. The non-transitory computer-readable medium of claim15, wherein restricting service by the first access node on the FDDcarrier to be for UEs that are relatively far away from the first accessnode comprises: determining that a distance of a UE from the firstaccess node is at least as short as a predefined threshold distance; andresponsive to the determining, causing the UE to be served by the firstaccess node on the TDD carrier rather than on the FDD carrier.
 17. Thenon-transitory computer-readable medium of claim 16, further comprisingsetting the predefined threshold distance at a level that helps tosituate the FDD coverage area at least partially between the TDDcoverage area and the coverage area provided by the second access node.18. The non-transitory computer-readable medium of claim 16, whereincausing the UE to be served by the first access node on the TDD carrierrather than on the FDD carrier comprises: if the UE is currently servedby the first access node on the TDD carrier rather than on the FDDcarrier, then continuing to serve the UE on the TDD carrier; and if theUE is currently served by the first access node on the FDD carrierrather than on the TDD carrier, then transitioning the UE from beingserved by the first access node on the FDD carrier to being servedinstead by the first access node on the TDD carrier.
 19. Thenon-transitory computer-readable medium of claim 15, wherein restrictingservice by the first access node on the FDD carrier to be for UEs thatare relatively far away from the first access node comprises:determining that coverage strength detected by a UE from the firstaccess node is at least as strong as a predefined threshold coveragestrength; and responsive to the determining, causing the UE to be servedby the first access node on the TDD carrier rather than on the FDDcarrier.
 20. The non-transitory computer-readable medium of claim 19,wherein the operations additionally include setting the predefinedthreshold coverage strength at a level that helps to situate the FDDcoverage area at least partially between the TDD coverage and thecoverage area provided by the second access node.